Are you tired of feeling tired? Do you often reach for that extra cup of coffee to power through the day? Well, you're not alone. Caffeine is a trusty sidekick that perks us up when we're feeling down.
But what does caffeine actually do to our bodies? It's more than just a quick energy boost — it's a complex, sneaky substance that can unexpectedly affect sleep, energy, and learning. So, buckle up, grab a fresh cup of joe, and let's dive into the wild world of caffeine!
When caffeine enters your body, it quickly goes to work. In as little as 15 minutes, it's fully absorbed by your gastrointestinal tract. Water and fat-soluble, it rapidly crosses the blood-brain barrier, peaking in your nervous system anywhere between 15 minutes and 2 hours. It then has an elimination half-life (how long it takes your body to remove 50% of its concentration) of between 1.5 and 9.5 hours, with an average of approximately 5 hours in most healthy individuals.
Caffeine's Impact on Sleep
As the day winds down and the sun sets, a little mastermind in your brain takes charge. The suprachiasmatic nucleus instructs your pineal gland to release a sleepy little hormone called melatonin. But don't let melatonin fool you. It's not the knockout punch for bedtime — it's just the starter pistol. Despite popular belief, melatonin's job is to signal that it's time to start winding down, not actually to induce sleep.
The molecule adenosine, whose increasing presence after 12–14 hours of wakefulness is responsible for the irresistible urge to sleep, is produced from adenosine triphosphate (ATP) decay, a vital part of energy generation. Without ATP, cells can't transfer energy from one location to another, making it impossible for organisms to grow and reproduce.
The human body recycles its weight equivalent in ATP every day, and since 20% of all energy we produce services brain functions, that results in a lot of ATP and, in turn, adenosine in the brain.
Under normal circumstances, it takes a full night's sleep of 8 hours for adenosine to be purged entirely of an adult's brain, but this is where caffeine comes in. For adenosine to have any effect, it must bind to receptor sites in the brain, but caffeine and adenosine share a very similar structure:
So whenever caffeine is in the brain, it will hijack the cells' adenosine receptors, binding itself and blocking the tiredness-inducing effects of adenosine. This is how caffeine gives you energy. It doesn't increase energy. Rather, it borrows energy by altering the time adenosine is released.
Caffeine's Impact on Energy
Adenosine is also partially responsible for controlling our energy levels by regulating heart rate, muscle contraction, and blood flow. It does this by interacting with cell-surface receptors on your endothelium (the inside lining of blood vessels, lymph vessels, and the heart) to produce relaxation.
Like its impact on adenosine in the brain, caffeine floods these cell-surface adenosine receptors. Essentially "…taking the chaperones out of the high school dance", blocking adenosine's dilating effects and causing a constriction of the blood vessels.
This vasoconstriction increases blood pressure, prompting the pituitary gland to assume crisis. It then triggers the fight-or-flight response — activating norepinephrine release, radically raising free epinephrine levels, and shifting the body into a state of alertness.
Caffine's Impact on Learning
As caffeine prevents adenosine's effects, it also allows energy-boosting neurotransmitters, such as dopamine, serotonin, glutamate, and acetylcholine, to flow freely. These newly released neurotransmitters help encourage neural activity and neuroplasticity, leading to better learning and memory.
The aforementioned spike in adrenaline caused by caffeine also improves learning since having a highly activated parasympathetic nervous system will significantly enhance memory and recall. The amount of caffeine needed to produce these effects varies from person to person, depending on body size and degree of tolerance.
I hope you found this article interesting. Click here for PART ONE, where we explore the history of Caffeine. I highly recommend Andrew Huberman’s podcast episode on Caffeine if you want additional information. Thanks for reading, and stay focused!
